The present invention relates generally to the field of computer backup storage and disaster recovery systems, and more particularly to computer backup storage and disaster recovery systems in which the backup system may be tested with current backed up data while data continues to be transferred from the primary system to the backup system.
Many businesses depend heavily on their computer systems and data. Loss of data or computer production time can be disastrous to a business entity. Accordingly, most businesses back up their data. In order to achieve maximum protection, many businesses have remote sites at which their data and computer systems are duplicated. In case of a disaster or other shut down at a primary site, operations can be resumed at the remote site with substantially no loss of time or data.
When a primary volume in a production site is mirrored to a secondary volume at a remote site, system users may desire to test a disaster situation by starting applications on a host at the remote site. The test is designed to simulate taking over functionalities of the production site. The applications at the remote site may read and write data on the secondary volume for the test. The data used for the test should be as realistic as possible and preferably real data. Data mirroring from the production site to the remote site needs to be resumed as soon as possible after the test.
There have been attempts to provide systems that enable tests of disaster situations. For example, in U.S. patent Publication 2003/0126107 A1, there is disclosed a system in which a replica volume of a secondary volume is prepared and used for the test. In that system, the replica volume is an exact copy of the secondary volume. Accordingly, the replica volume is the same size as the secondary volume even though the amount of data used for the test is in all likelihood only a small part of the total amount of data in the secondary volume. Moreover, copying the entire secondary volume is a time consuming process. Additionally, some users may need to use the same volume as is used in the case of a disaster, which is not possible with the system of the U.S. publication.
An alternate attempted solution is disclosed in U.S. Pat. No. 6,092,066 in which the secondary volume is used for testing. Remote mirroring from the primary volume is suspended during the test. At the conclusion of the test, the primary and secondary volumes are resynchronized. The patented system prepares bitmaps of the primary and secondary volumes and exchanges the bitmaps in order to resynchronize the volume. If a disaster happens during the test, data written on the primary volume will be lost before it is transferred to the secondary volume. Additionally, it takes a long time to send data updated on the primary and secondary volumes during the test from the primary volume to the secondary volume until they are resynchronized with each other.